Abstract
The antifungal mode of action of thymol was investigated by a chemical-genetic profile analysis. Growth of each of ˜ 4700 haploid Saccharomyces cerevisiae gene deletion mutants was monitored on medium with a subinhibitory concentration (50 μg/ml) of thymol and compared to growth on non-thymol control medium. This analysis revealed that, of the 76 deletion mutants with the greatest degree of susceptibility to thymol, 29% had deletions in genes involved in telomere length maintenance. A telomere restriction fragment (TRF) length assay showed that yeast exposed to a subinhibitory concentration of thymol for 15 days had telomere size reductions of 13–20% compared to non-thymol controls. By accelerating telomere shortening, thymol may increase the rate of cell senescence and apoptosis. Furthermore, real-time RT-PCR analysis revealed approximately two-fold reductions in EST2 mRNA but no change in TLC1 RNA in thymol-treated S. cerevisiae relative to untreated cells. EST2 encodes the essential reverse transcriptase subunit of telomerase that uses TLC1 RNA as a template during addition of TG(1–3) repeats to maintain telomere ends. This study provides compelling evidence that a primary mode of thymol antifungal activity is through inhibition of transcription of EST2 and thus telomerase activity.
Acknowledgments
This work was supported by Discovery Grants from Natural Sciences and Engineering Research Council (NSERC) of Canada to A.G. and M.L.S., and Ministry of Science, Research and Technology, Iran to E.D. We would like to thank Dr Janis Shampay (University of California) for generous gift of pYt103 plasmid. We also thank Md Alamgir, M. Jessulat, B. Samanfar, I. Galvan and D. Lafontaine for valuable technical advice.
Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and the writing of the paper.